Color Correction Versus Color Adjustment

Take a virtual trip to Alaska to learn color correction and adjustment techniques!

Not all images need color correction, but you may want to adjust their color anyway…

The term color correction implies that there is something incorrect about the color in the image. Common color corrections involve removing color casts from neutral white highlights or fixing the color balance in skin tones. These types of color changes represent true color corrections, for if you do not make these color corrections, the color in your image will look and be wrong.

Following are some examples of typical color scenarios. We'll explore situations in which color needs to be corrected, and one where color can be adjusted to create a mood.

Highlight-Based Color Corrections

Here is this a photo of Ellie Guttman of Washington DC, out enjoying a day on the water in Alaska. A blue color cast (common in outdoor scenes) pervades the photo. We know there is a blue color cast by measuring the RGB values in the what is supposed to be the diffuse white highlight area found in Ellie's cap.

Click the image to download a TIFF to work with.

A neutral white highlight should have equal RGB (red, green, and blue) values. Here you can see that the RGB point #1 values are 235, 238, and 241 respectively. The blue value (241) is significantly higher than the red and green values of 235 and 238. This is proof of the blue color cast.

Using the Curves dialog and the 235 red value as the target highlight value, we lower the blue and green highlight values until they are 235, and then make a similar adjustment in the midtone.

Step-by-Step

1. Open and duplicate the Ellie Boot_Start.tif image that you downloaded above. Name the duplicate Ellie Boot_Finish.

2. Activate your Color Sampler tool (found under the Eyedropper tool in the Tools palette or by pressing Shift+I). This tool will allow you to record and monitor up to four RGB value sets. Also activate the Info palette (Window > Info or F8) and set the Color Sampler tool's Sample Size to 3 x 3 Average.

3. Locate and click, with the Color Sampler tool, on the white neutral diffuse highlight in Ellie's cap. A Color Sampler point is placed where you click on Ellie's cap. The RGB values for this point are recorded as point #1 and displayed at the bottom of your Info palette. Your RGB value set should be close to the one I measured above (about 235, 238, 241).

4. Activate your Curves dialog (Image > Adjustments > Curves or Ctrl/Command+M).

5. Activate the Blue channel curve form the Curves Channel menu.

6. Click on and pull the highlight end of the Curve down until the blue value for point #1 in your Info palette equals the Red value (here 235). Then click and drag the midpoint of the Blue channel down an amount equal to the adjustment you made on the highlight point.

Note: This midtone adjustment is made assuming that the blue color cast you identified in the highlight is pervasive throughout the image's tonal range. While this is not always the case, it is a shortcut assumption that is often useful.

7. Now, activate the Green channel curve, and perform a similar adjustment to this channel. Click on and pull the highlight end of the Curve down until the Green value for point #1 in your Info palette equals the Red value (235). Then click and drag the midpoint of the Green channel down an amount equal to the adjustment you made on the highlight point.

8. Click the OK button to apply these Curves changes. Now compare your Ellie Boot Start and Finish images.

The results of the highlight-based correction are:

	1. The neutral white highlight pops. 2. The yellow boot has better saturation. 3. Ellie's skin looks healthier. 4. The original subtle green in Ellie's coat shows through. 5. There is an overall reduction in the blue cast across the image, resulting in overall improvement of the image ... even the spruce trees in the background look better (more saturated).

We didn't make a huge color correction here, but you can see that the results are a noticeable improvement.

Skin Tone Adjustments

Another common, and critical type of color correction is the RGB ratios in skin tones.

Here we have Nancy Lasater, Ellie's mom, also out on the water in Alaska.

Click the image to download a TIFF to work with.

The RGB values of her face show that blue (206) is above the green (202). This violates the general facial skin tone rule that R > G > B (in humans anyway, Klingons are another matter). Using the Curves dialog, we lower the overall blue values until Nancy's skin tones values conform with the R > G > B rule.

Step-by-Step

1. Open and duplicate the Nancy_Start.tif image that you downloaded above. Name the duplicate Nancy_Finish.

2. Activate your Color Sampler tool and Info palette, and set the Sample Size to 3 x 3 Average as you did for the previous photo.

3. Locate and click on the a well-lit portion of Nancy's face (I used a place on Nancy's chin above) with the Color Sampler tool. A Color Sampler point will be placed where you click on Nancy's face. The RGB values for this point will be recorded as point #1 and displayed at the bottom of the Info palette. Your RGB value set should be close to the one measured above (about 237, 202, 206). Note the Green is well below the Red (as it should be if R > G > B). The blue is the problematic value, so you will want to lower the blue value.

Note: For the purposes of brevity, you are using only one Color Sampler point. However, you may want to locate two or three points (I often do) to make sure that you are making an overall correct adjustment. Creating multiple Color Sampler points will create multiple Info Palette monitoring points as well. One of the advantages of using the Color Sampler tool is that you can measure, record, and monitor values of up to four separate points.

4. Activate your Curves dialog (Image > Adjustments > Curves or Ctrl/Command+M).

5. Activate the Blue channel curve form the Curves Channel menu.

6. Press your Ctrl (PC) or Command (Mac) key and click on top of the Color Sampler point you placed on Nancy's face. This will create a control point on the Blue Curve at the point in the tonal range where the Color Sampler point is placed.

Note: If you are using multiple Color Sampler points, you can create and edit several controls points. But first try editing just one point while monitoring the RGB values on the other Color Sampler points.

7. Now click on the blue channel control point on the curve and drag it down while you monitor the Blue value in displayed in Color Sampler point #1. Lower the Blue curve until the Blue value is well separated from the Green value.

Note: How much separation you create will depend upon the image and the current Red and Green values. A good starting place on many images is to create a 5:4:3 ratio between Red, Green, and Blue values (in well-lit areas of the image). If this seems too much separation, try a 7:6:5 ratio. In this image, since Nancy has red skin and hair, I have allowed the red value to be more separated from the green and blue values than in other images. You may want to place and monitor a Color Sampler point in a neutral area of your image, such as the gray under jacket I have sampled here, to help you determine how much you adjust the channels.

8. Click the OK button to apply your Curves changes. Now compare your Nancy Start and Finish images.

The results of this color correction are:

	1. Nancy's skin tone looks more natural. She looks less like she is turning blue from lack of oxygen. 2. Nancy's gorgeous red hair really pops now once all that excess blue is removed! 3. The orange in Nancy's jacket has better saturation.

Both of the above scenarios are examples of honest-to-goodness color corrections. The color values were wrong, and when they were corrected, the images showed noticeable improvements.

Color Adjustments

As we mentioned earlier, not all color changes represent color corrections. You may want to change the color in an image to change its mood or its emphasis, with neither the original or the final image being correct, just different from each other.

Here is a photo I shot of the southern Kenai Mountains in Alaska on an early morning kayak trip.

Click the image to download a TIFF to work with.

The early morning light was quite yellow and projected a very calm mood. This image is just fine the way it is; there is nothing wrong with the color. But we can change its mood by reducing the yellow cast and creating a more neutral or even a bluish cast.

This can be accomplished by equalizing or neutralizing the data in histograms using the Levels dialog in Photoshop.

Step-by-Step

1. Open and duplicate the Kenai_Start.tif image you downloaded above. Name the duplicate Kenai_Neutralize.

2. Activate your Levels dialog (Image > Adjustments > Levels or Ctrl/Command+L).

3. In the default RGB Channel view, click and drag the RGB shadow slider from its far left position to the right into the beginning of the shadow data of the image.

Note: This will darken the shadow areas of the image, thereby increasing the overall contrast of the image. If you want to make the darkest area solid black (with no detail), drag the shadow slider further into the shadow data portion of the histogram.

4. View the histogram data of all three individual channels. Note how the starting Blue channel highlight is offset to the left of the Red and Green channels' highlight data. This is the source of the yellow (red + green) color cast.

5. Select the Blue channel from the Levels Channel menu.

6. Drag the highlight slider of the Blue channel to the left, until it is just under the beginning of the highlight end of the histogram data.

Note: This will place the beginning of the Blue channel histogram highlight data in the same location as the Red and Green channels, thereby neutralizing the highlight data and removing much of the yellow (red + green) color cast from the image.

7. Click the OK button to apply your Levels changes. Now compare your Kenai Start and Neutralize images.

We can further enhance the blue shift using Levels or Curves. Using Curves is my preferred method.

1. Duplicate the Kenai_Neutralize image you just created above. Name the duplicate Kenai_Blue.

2. Activate your Curves dialog (Image > Adjustments > Curves or Ctrl/Command+M).

3. Activate the Blue channel curve form the Curves Channel menu

4. Now, click on the midpoint of the Blue channel curve and drag it up 10%.

5. Click the OK button to apply your Curves adjustment. Now compare your Kenai Start, Neutralized, and Blue images.

Note how this last Curves adjustment enhances the blue value in both the sky and water. Also be aware that you can create selections of specific portions of an image, such as the sky and/or the water here, and adjust the color values for only that/those portion(s) of the image.

These two color adjustments do not represent corrections, as there was nothing wrong with the images. But they certainly represent significant color adjustments.

Color Correction and Adjustment Tips

Deciding on Color Changes

A good approach to making color changes is to ask yourself the following questions and apply these actions.

	1) Is there any color correction that needs to be applied to this image? If so determine (using your Info palette and histograms) what those corrections are. 2) Make any needed color corrections prior to proceeding with any color adjustments. 3) What, if any, non-correction-based color adjustments might you like to make? Decide which tools and methods you should use to accomplish those corrections.

Tip: Always apply the change adjustments to copies of your original images so you can always return to the original. This is especially true if the images belong to someone else!

Taz's Top Five Color Correction Tools

	1) The Info palette provides me foolproof RGB and CMYK image values ... the Info palette will not lie! 2) The histogram in the Levels dialog shows me where the data is and how it is distributed. 3) The highlight and shadow sliders in the Levels dialog allow me to adjust the highlight and shadow points while viewing an image's histogram data. 4) The Curve dialog allows me to make specific image corrections anywhere within the tonal range of an image. 5) The highlight and midtone Eyedropper tools in both Levels and Curves dialogs allow me to make fast and accurate preset highlight and shadow adjustments to images, especially when I am working with target-based color corrections.

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